1. Field of the Invention
This invention relates to a digital image acquisition system having a portrait mode for generating an image of a foreground object against a blurred background, and a corresponding method.
2. Description of the Related Art
In digital cameras the depth of field (DOF) is typically much greater than for conventional cameras due to the image sensor being somewhat smaller than a 35 mm film negative. This means that portrait images, in particular, will tend to have the background in sharp focus, which may not be desirable as the photographer may wish to emphasize the person's face and de-emphasize the background of the picture. This problem can be corrected by careful photography combined with careful use of camera settings. Alternatively, portrait images are often blurred manually by professional photographers using image processing algorithms. A blurring algorithm may apply various techniques using convolution kernels to create the blurring effects. These effects are normally added on a desktop computer after an image has been captured. This may involve manual intervention and be time-consuming.
US 2003/0052991 discloses to adjust image brightness based on depths of different image features. A digital camera simulates the use of fill flash. The camera takes a series of photographs of a scene at various focus distances. The photographs are stored, along with their corresponding focus distances. The photographs are analyzed to determine distances to objects at various locations of the scene. Regions of a final photograph are selectively adjusted in brightness based on distance information to simulate the effect that would have resulted had fill flash been used.